How did dogs become man’s best friend? Eye contact, study suggests.

A student playing with Hook, a Labrador Retriever. His gazing behavior increased his owner’s urinary oxytocin (experiment 1) but his gazing behavior did not increase after administered oxytocin (experiment 2).

Not exactly, but new research suggests a direct correlation between eye contact and dog-human bonding. In a study published Thursday in Science, Japanese dog cognition experts show how prolonged “mutual gaze” fosters emotional bonds that appear to be correlated with a release of hormones in both dogs and and humans.

Humans have kept domesticated dogs for millennia, but the phrase “man’s best friend” only entered our vernacular in recent centuries. It’s a well-earned title, but an inexplicable one: for reasons unclear, no other interspecies companionship comes close.

To better understand the neurobiology behind human-dog companionship, a team of researchers from Azabu University in Sagamihara, Japan, placed a number of canine participants in a room with their owners. They instructed owners to touch, talk to, or gaze at their pets for a period of 30 minutes. When the time was up, researchers took urine samples from both pet and owner, which they tested for oxytocin levels. Oxytocin is sometimes called the “love hormone” – during mammalian reproduction and childbirth, it acts as a neurotransmitter, sending positive feedback to the brain. It is also associated with pair bonding.

“We think that in terms of nurturing or care taking, the human-dog bonding and parent-infant bonding is comparable,” co-author Takefumi Kikusui said. “Both of them have a same oxytocin-mediated positive loop.”

Surprisingly, Dr. Kikusui’s team found that simple eye contact was better at raising oxytocin levels than vocal communication or physical contact. So as much as your dog probably appreciates a good scratch behind the ear, eye contact has a deeper association with bonding.

To determine the origin of this bonding mechanism, researchers replicated the experiment with wolves – the closest living relative to the domestic dog. In those trials, eye contact did not result in significant oxytocin release. In other words, mutual-gaze bonding must have developed after modern dogs diverged from their wolf ancestors. Evan MacLean, a Duke University researcher studying animal cognition, says that dogs and humans could have coevolved this form of communication during domestication – which is thought to have occurred between 11,000 and 16,000 years ago.

“It’s relatively fast in the scheme of things,” Dr. MacLean said. “But under artificial selection, things can happen very quickly. For example, most of the dog breeds we know today, in all their splendid diversity, are the product of the Victorian era.”

In the second phase of the experiment, researchers gave dogs a nasal spray of oxytocin and placed them in a room with their owners and some strangers. Female dogs responded by gazing at their owners longer, which in turn raised the oxytocin levels of the owners. There was no discernable difference in males, for reasons still unclear, Kikusui says.

But for many canine enthusiasts, the research begs a more obvious question: will my dog love me more if I stare at it?

“We think that dogs naturally have ability to show mutual gazing with humans,” Kikusui said. “But of course not all the dogs easily show this behavior. My guess is that if the owner and dog spend intensive and positive communication time – such as talking to the dogs, petting, giving treats – dogs usually pay attention to the owner.”

“Gaze has different meanings in different situations,” MacLean said. “So it’s great to gaze lovingly at your dog when it’s a natural bonding moment, but I wouldn’t spend too much time forcing this type of interaction outside of natural contexts. Believe me, most dogs will spend plenty of time looking at you quite naturally.”